A variety of methods for preparation of polysuccinimide and subsequent hydrolysis to polyaspartic acid (or salts) have been described in the literature and patents. In addition methods of preparation of copolymers of polyaspartic acid have also been reported in the literature.
In a series of patents, Koskan et al. discloses a method for thermal polymerization of aspartic acid in a fluidized bed to form polysuccinimide which is then hydrolyzed to polyaspartic acid (sodium salt) using sodium hydroxide (U.S. Pat No. 5,057,597; U.S. Pat No. 5,116,513; U.S. Pat. No. 5,152,902 and U.S. Pat. No. 5,221,733). Uses of polyaspartic acid as calcium carbonate, calcium and barium sulfate and calcium phosphate scale inhibitors are also described in these patents.
Production of polysuccinimide and polyaspartic acid (and salts) from maleic anhydride, water and aqueous ammonia is taught in patents by Koskan and Meah (U.S. Pat. No. 5,219,952 and U.S. Pat. No. 5,296,578). Polysuccinimide is produced in at least 90% of theoretical yield by heating the maleic anhydride, water, ammonia mixture at 220.degree.-260.degree. C. In U.S. Pat. No. 4,839,461, Boemke teaches the production of a polyaspartic acid salt by the reaction of maleic acid and aqueous ammonia at 120.degree.-150.degree. C. followed by hydrolysis of the resulting acid with metal hydroxides or ammonium hydroxide. A process is disclosed (in U.S. Pat. No. 5,288,783) for the preparation of a salt of polyaspartic acid by reacting maleic acid and ammonia in a molar ratio of 1:1-..2.1.!. .Iadd.2:1 .Iaddend.at 190.degree.-350.degree. C. for a time followed by hydrolysis of the resultant polymer using metal or ammonium hydroxide.
Fox and Harada ("A Laboratory Manual of Analytical Methods of Protein Chemistry Including Polypeptides," P. Alexander and H. P. Lundgren, Ed., Pergamon Press, Elmsford, N.Y., 1966, p127-151) thermally polymerized aspartic acid using 85% phosphoric acid and polyphosphoric acid to obtain improved yields and higher molecular weight polysuccinimide. Neri et al J. Med Chem., 16, 893 (1973)! also used phosphoric acid to facilitate condensation of aspartic acid under vacuum and in a thin film process to obtain high molecular weight polysuccinimide.
Aspartic acid has been thermally copolymerized simultaneously with seventeen amino acids at ..175.degree.180.degree..!. .Iadd.175.degree.-180.degree. C. .Iaddend.to obtain polymers of molecular weight range 3000-9000...S..!. .Iadd.(S. .Iaddend.W. Fox and K. Harada, J. Am. Chem. Soc., 82, 3745 ..(1960).!.!. .Iadd.(1960).) .Iaddend.Copolymers of aspartic acid with glutamic acid and terpolymers of aspartic acid, glutamic acid and alanine have also been reported in the literature (S. W. Fox and K. Harada, "A Laboratory Manual of Analytical Methods of Protein Chemistry Including Polypeptides," P. Alexander and H. P. Lundgren., Ed., Pergamon Press, Elmsford, N.Y., 1966, p 127-151). Lysine has been copolymerized with aspartic acid and other amino acids and with non-amino acid monomers such as caprolactam, succinic ..acid,.!. .Iadd.acid and .Iaddend.terephthalic acid (S. W. Fox and K. Harada, vida supra).
Harada K.Harada, J. Org. Chem., 24 1662 (1959)! reported preparation of polysuccinimide by thermally condensing precursors of aspartic acid such as monoammonium malate, monoammonium maleate, maleamic acid and combinations of asparagine and malic acid, maleamic acid and malic acid, monoammonium malate and maleamic acid, malic acid and ammonium maleamate, maleic anhydride and ammonium maleamate, fumaric acid and ammonium maleamate.
Copolyamino acids of aspartic acid are prepared by Harada, et al (U.S. Pat. No. 4,590,260) by thermally polymerizing at least one amino acid with at least one precursor of aspartic acid such as monoammonium malate, ammonium salts of maleic or fumaric acid, an ammonium salt of maleic, malic, fumaric acid monoamide or diamide and hydrolyzing the reaction mixture under neutral or alkaline conditions.
Harada and Shimoyama (U.S. Pat. No. 4,696,981) prepared polysuccinimide from precursors of aspartic acid such as monoammonium, diammonium, monoamide, diamide and monoamideammonium salts of malic, maleic and fumaric acid and mixtures of these materials by irradiating them with microwaves. The resulting polysuccinimide was hydrolyzed to form polyaspartic acid. Similarly mixtures of at least one amino acid and precursors of aspartic acid were irradiated with microwaves followed by hydrolysis to produce copolyamino acids of aspartic acid (Harada and Shimoyama, U.S. Pat. No. 4,696,981).
German laid open document No. 4217847 discloses preparation of aspartic acid-amino acid copolymers, prepared by thermal condensation of L-aspartic acid with other amino acids followed by hydrolysis of the condensation reaction mixture. ..
.!. These polymers were used to prevent encrustation during sugar juice evaporation.
Modified polyaspartic acids are prepared by polycocondensation of aspartic acid with carboxylic acids (monobasic and polybasic) and anhydrides, ..hydroxycarboxlic.!. .Iadd.hydroxycarboxylic .Iaddend.acids, alcohols, amines, alkoxylated alcohols and amines, amino-sugars, carbohydrates, sugar carboxylic acids, and non-protein forming amino-carboxylic acids (Ger. laid open document No. 4221875).
U.S. Pat. No. 5,286,810 discloses the preparation of higher molecular weight copolymers of polyaspartic acid which are suitable for the inhibition of scale deposition by reacting maleic acid and ammonia in stoichiometric excess with a diamine or a triamine at ..120.degree.350.degree. C.!. .Iadd.120.degree.-350.degree. C.Iaddend.. The resulting copolymers of polysuccinimide are converted to a salt of the copolymer of polyaspartic acid by hydrolysis with a hydroxide.
Copolymers of polyaspartic acid are also made by reaction of part of the succinimide units in polysuccinimide with amines followed by hydrolysis of the remaining succinimide units to form aspartic acid units (Fujimoto et al., U.S. Pat. No. 3,846,380; ..Jaquet.!. .Iadd.Jacquet .Iaddend.et al., U.S. Pat. No. 4,363,797).
Copolymers of polyaspartic acid are prepared by making maleic half esters followed by addition of an equivalent of ammonia and an amine and heating to 120.degree.-350.degree. C. When an equivalent of alcohol is distilled off, a copolymer of polysuccinimide is formed which is hydrolyzed with hydroxides to form amide copolymers of polyaspartic acid (Wood, U.S. Pat. No. 5,292,858).